The present invention relates to environmental control systems, and more particularly such systems having parallel compressors and methods for operating the same.
Environmental control systems (ECS) are utilized on various types of aircraft for several purposes, such as air supply systems and/or cabin conditioning systems for the aircraft. For example, components of the ECS may be utilized to remove heat from various aircraft lubrication and electrical systems and/or used to condition aircraft cabin air. The cabin air conditioner includes one or more cabin air compressors (CACs) which compress air entering the system from an outside source or from a ram air system. The compressed air is delivered to an air cycle system and/or a vapor cycle system to bring it to a desired temperature then delivered to the aircraft cabin. After passing through the cabin, the air is typically exhausted to the outside. The CACs may be driven, for example, by air-cooled electric motors.
In an ECS utilizing two CACs, it is desirable to operate both CACs at relatively identical flow levels, known as operating at nearly identical operating points on a compressor map, or symmetrical operation. Failure to do so may result in various inefficient or undesirable operational characteristics, such as compressor surging, that can lead to unstable airflow. In an effort to monitor the operating points of the CACs, various sensors are employed. Inherent errors associated with the sensors may lead to uncertainty of operating points. Various other reasons lead to asymmetric operation, thereby causing inefficient and/or undesirable operation of the CACs.